System of designing a guide tool and/or surgical kit tools and/or an implant comprising a positioning mark

ABSTRACT

A method for designing an implant includes designing a contour curvature of the implant so that an articulate surface of the implant is designed to correspond to a simulated healthy cartilage surface reconstructed from a 3D model based on one or more images taken with MRI or CT-scanning of a damaged cartilage surface of a joint; and providing a positioning mark on a surface of the implant. The positioning mark is provided such that the positioning mark is parted from the center of the implant to be visible for a surgeon and is adapted to be used for indicating a rotational position of the implant to the surgeon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending prior U.S. patent application Ser. No. 14/784,376, filed Oct. 14, 2015, which is the National Stage of International Application No. PCT/EP2013/057847, filed Apr. 15, 2013. The contents of each of these applications are incorporated herein in their entirety.

FIELD OF THE INVENTION

This invention relates in general to the field of designing tools for use during replacement of damaged cartilage in an articulating surface in a joint all comprising positioning marks. The present invention also confers to tools made using the design method according to the invention.

BACKGROUND General Background

Pain and overuse disorders of the joints in the body is a common problem. The weight-bearing and articulating surfaces of the knees, and of other joints, are covered with a layer of soft tissue that typically comprises a significant amount of hyaline cartilage. The friction between the cartilage and the surrounding parts of the joint is very low, which facilitates movement of the joints under high pressure. The cartilage is however prone to damage due to disease, injury or chronic wear. Moreover it does not readily heal after damages, as opposed to other connective tissue, and if healed the durable hyaline cartilage is often replaced by less durable fibrocartilage. This means that damages of the cartilage gradually become worse. Along with injury/disease comes a problem with pain which results in handicap and loss of function. It is therefore important to have efficient means and methods for repairing damaged cartilage in knee joints.

The advantages of implants have stimulated a further development of smaller implants that can be implanted with less invasive surgery. In this development there has also been an effort to achieve small joint implants, suitable for repair of a small cartilage injury that have a minimal influence on the surrounding parts of the joint. In the surgical operation of implanting such small implants it is critical that the implant is positioned in a precise manner. If the implant is offset from its intended position it may cause an increased wear or load on the joint. For example, if the implant is tilted this may result in an edge that projects above the cartilage surface and causes wear on the opposing cartilage in the joint. Another example is the case that the implant is placed in a too shallow position, which may result in a too high top of the implant that causes the joint to articulate in an uneven manner and increase the load on an opposing point of the joint. For the patient, also small misplacements or deviations from an ideal position may result in pain, longer time for convalescence or even a surgical operation being done in vain and making it more difficult to repair the damage in the joint. A large burden is therefore placed on the surgeon not to misplace or misfit the implant. There is therefore a need for well fitting implants as well as tools that are designed to relieve and support the surgeon in the implant surgery.

Specific Background

The design of the implant and the surgical tools, in other words, the design of the surgical kit is crucial for the outcome of the implants life-time in a joint. Also, the parameters for designing are of uttermost importance for the result in these operations. Small differences in the design can make a huge difference in fit and life-time of an implant in the body, convalescence time for the patient, economic values due o surgery time, success of operations, also the number of successful operations will increase and the working conditions for the surgeon will be improved if the designing parameters are selected right etc.

There is a need for a design method for a guide for use during repair of a cartilage damage which is more user friendly for the surgeon than the guide tools known from prior art. There is a need for a guide tool which allows for small surgical cuts and also a design method which allows for producing small guide tools which still are stable and easy to use for the surgeon allowing for precise insertion of implants in a joint.

Prior Art

A prior art document which describe the design of an orthopedic implants and corresponding tools is for example:

EP2389905 A1 shows a design method for designing an individually designed surgical kit.

OBJECT OF THE INVENTION

The general object of the invention is to solve the problem of designing an improved guide tool for use during cartilage repair for replacing damaged cartilage and also an improved design method for designing inserts tools and also implants. The design of the guide tool and the insert tools and the implant makes the surgical operation safer and results in better fitting implants, less surgeon dependent operation procedures and faster recovery of the patients after surgery due to that the implant guide can be made smaller and neater using this design method.

SUMMARY OF THE INVENTION

The object of the invention is achieved with a system for designing a guide tool and/or a surgical kit and or an implant.

The present invention relates to a design method for designing a guide tool 12 comprising a guide channel 54 for use during cartilage repair in a joint wherein the design method comprises;

-   -   a step for placement of a positioning mark 500 on the guide tool         wherein the positioning mark 500 is designed to be aligned with         the center 503 of said guide channel in a determined joint axis         501 direction and thereby indicating a placement direction of         the guide tool 12 in relation to the selected joint axis 501         during use of the guide tool 12

In another embodiment the present invention relates to a design method for designing a guide tool 12 which is intended for use during cartilage repair in a joint wherein the design method comprises;

-   -   a step for placement of a positioning mark on the guide tool         which indicates a placement direction of the guide tool in         relation to the joint.

In another embodiment, the present invention relates to a design method for designing a guide tool 12 which is intended for use during cartilage repair in a joint wherein the design method comprises;

-   -   a step for placement or design of a positioning mark on the         guide tool wherein the position mark indicates a placement         direction of the guide tool in relation to the joint wherein the         placement direction is used during placement of the guide tool         12 in the joint.

The present invention further relates to the different alternatives described below in any combination;

a design method for designing a guide tool 12 wherein the step for placement of the positioning mark of the guide tool in comparison to the joint where the guide tool is to be placed an in relation to a guide channel comprised in the positioning body 11 of the guide tool 12, and wherein the position mark placed on a top surface 52 indicate to the surgeon of how to place the guide tool on the joint during cartilage repair by that the placement of the positioning mark indicates a placement direction of the guide tool in relation to the joint.

A design method for designing a guide tool 12 wherein the placement of said positioning mark is on a top surface 52 or top of the guide channel or a surface which is visible for the surgeon during usage.

A method of designing a guide tool 12 according to the invention further comprising the steps of:

-   -   generating information of a cartilage damage     -   using information about said cartilage damage to determine size         and shape of implant and/or size and shape of cartilage and/or         bone needed to be removed in order to repair said damage     -   using information about said cartilage damage to determine size         and shape of a cartilage size and spread of a contact surface 52         of the guide tool 12 designed to follow the shape and curvature         of the individual cartilage in said joint     -   designing a guide tool 12 based on information of cartilage         damage and the determined size and shape of implant and/or size         and shape of cartilage and/or bone needed to be removed in order         to repair said damage.

A method of designing a guide tool 12 wherein the direction pointed out by the position mark in relation to the joint where the guide is a direction such as; anterior or posterior, right lateral or left lateral, dorsal or ventral, proximal or distal in relation to the placement of the guide tool 12 in a joint.

A method of designing insert tools designed to comprise positioning marks which is designed to be aligned with the positioning mark of the guide tool 12 when the insert tools are placed in the guide tool in start position, indicating the correct rotational start position of the insert tools to the surgeon during use of the guide tool and insert tools during surgery.

A guide tool or insert tools or an implant designed according to any of the preceding claims

The design method of the invention may comprises the basic blocks of:

I. Determining physical parameters for a cartilage damage in a joint and then using this information in order to;

II. Generate design parameters of a medical implant 10.

III. Generate design parameters of a guide tool 12 for use during implantation of said implant.

The physical parameters as well as the design parameters are represented as digital data that is processed or generated by specifically designed computer program code portions executed in a data processing system. The system may be fully automated or may comprise portions of computer supported manual steps of for example selections. The design parameters resulting from the process are stored in a format suitable for use as input in an automated manufacturing process.

IV. Determine a positioning mark placement which placement helps the surgeon to determine the orientation of the placement of the guide tool in a joint and wherein the positioning mark for example may be chosen to be placed in a position on the guide tool which indicate an orientation selected from a position or direction on the patient which is known for the surgeon and based on the anatomy of a patient selected, for example selected from anterior or posterior, right lateral or left lateral, dorsal or ventral, proximal or distal orientation or axis direction.

and wherein blocks II-IV of the described design method above can be performed in any desired order.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be further explained with reference to the accompanying drawings which are exemplified embodiments according to the invention and not limiting the scope of the invention:

FIG. 1 schematically illustrates parts of the design process according to an embodiment of the inventive concept for designing a surgical kit.

FIG. 2. Shows a medical implant comprising a positioning mark placed using a guide tool according to the invention and wherein the positioning mark is placed in an anterior position in relation to a knee joint.

FIG. 3a-3b . Shows a medical implant according to the invention

FIG. 4A shows a guide tool comprising a positioning mark placed on top of the guide channel in anterior direction (compared to the relation of placement of the guide tool in the joint and in relation to the guide channel).

FIG. 4B shows an insert tool, in this example a reamer guide placed inside the guide channel of the guide tool in a start position and where the positioning mark of the guide channel and the positioning mark of the insert tool are aligned.

FIG. 5 shows a guide tool according to the invention placed on the cartilage in a joint and further comprising a height adjustment insert tool

FIG. 6 shows a guide tool according to the invention placed on the cartilage in a joint and further comprising a height adjustment insert tool placed in start position inside the guide channel, and wherein the positioning mark of the guide tool and the positioning mark of the height adjustment insert tool are aligned and wherein it is shown that the center of the guide channel is aligned with the positioning markings 500 in an anterior direction of a knee joint.

FIG. 7 shows a guide tool according to the invention placed on the cartilage in a joint and further comprising an implant dummy insert tool 36 placed in start position inside the guide channel 54, and wherein the positioning mark 500 of the guide tool 12 and the positioning mark 500 of the implant dummy 36 are aligned and the positioning mark on the implant dummy is placed on top of the implant dummy shaft.

FIG. 8 shows another view of a guide tool according to the invention placed on the cartilage in a joint and further comprising an implant dummy insert tool placed in start position inside the guide channel, and wherein the positioning mark of the guide tool and the positioning mark of the implant dummy tool are aligned and the positioning mark on the implant dummy is placed on top of the implant dummy shaft.

FIG. 9 shows a guide tool according to the invention placed on the cartilage in a joint and further showing a view how it looks like when the height adjustment tool 504 has been used inside the guide channel together with a reamer and/or drill to make a recess in a desired size and depth wherein the implant according to the invention can be placed.

FIG. 10 shows a guide tool according to the invention placed on the cartilage in a joint and further showing how the positioning mark of the guide tool is used to make a mark on side of the recess wherein the implant is to be placed in order to know in which direction the implant is to be placed in the recess when the guide is removed before placing the implant in the joint.

FIG. 11 shows a medical implant comprising a positioning mark according to the invention and wherein the direction of the positioning mark of the implant also is indicated on the cartilage surface due to previous guidance using the guide tool according to the invention during surgery.

FIG. 12 shows an exemplified embodiment of a guide tool and insert tools and implant designed using the design method according to the present invention.

FIG. 13a-b shows exemplified embodiments of the guide tool according to the invention

DETAILED DESCRIPTION OF THE INVENTION

Design Method

The present invention is directed to a system, comprising a method, apparatus and computer programs, for designing a guide tool 12 comprising a positioning mark 500, and/or medical implant comprising a positioning mark 500, and/or associated tools comprising positioning marks and wherein said guide tool 12 insert tool 502 and implant 10 all comprises a positioning mark 500 marking out the same direction or axis in relation to the joint during use when replacing damaged cartilage in a joint. The associated set of tools is devised for the placement of an implant that replaces damaged cartilage in a joint and is adapted to the specific implant as well as a specific joint for which the implant is intended. The surgical kit provided by the present invention has the effect that successful implant insertion is less dependent on surgical circumstances and the skills of the surgeon compared to previously known implants. Due to the design and the function of using the positioning marking in guide tool and/or implant and/or inert tools gives improved implantation precision and a precise desired placement of the implant in the joint every time. The precision of the surgery is “built in” into the design of the tools.

FIG. 1 shows an example of a surgical kit designed according to a method of one embodiment of the present invention. This particular exemplifying embodiment of a surgical kit according to the invention is especially adapted for cartilage replacement at the femur of a knee joint. The invention may however be applied for cartilage replacement in an articulating surface in any other joint in the body, e.g. elbow, ankle, finger, hip, toe and shoulder. The guide tool 12 according to the invention may be equipped with a guide-channel 13 and a a positioning body 11 and may be used together with an implant 10, and a drill guide 8, a cutting tool 6, which in this exemplifying embodiment is a punch, a drill-bit 8, preferably equipped with a depth gauge 1 and/or a reamer-bit 4, preferably equipped with a depth gauge 3, and/or a hammer tool 35 and/or a reamer guide 28, and/or implant dummy 36. The details of examples of insert tools 502 which may be used inside the guide tool 12 are further described and exemplified below.

FIG. 1 schematically illustrates the design process according to an embodiment of the inventive concept for designing a guide tool and/or insert tools 502 and/or implant 10.

The design system comprises the basic blocks of:

I. Determining physical parameters for a cartilage damage in a joint and then using this information in order to;

II. Generate design parameters of a medical implant 10.

III. Generate design parameters of a guide tool 12 for use during implantation of said implant.

The physical parameters as well as the design parameters are represented as digital data that is processed or generated by specifically designed computer program code portions executed in a data processing system. The system may be fully automated or may comprise portions of computer supported manual steps of for example selections. The design parameters resulting from the process are stored in a format suitable for use as input in an automated manufacturing process.

IV. Determine a positioning mark placement which placement helps the surgeon to determine the orientation of the placement of the guide tool in a joint and wherein the positioning mark 500 for example may be chosen to be placed in a position on the guide tool which indicate an orientation selected from a position or direction on the patient which is known for the surgeon and based on the anatomy of a patient selected, for example selected from anterior or posterior, right lateral or left lateral, dorsal or ventral, proximal or distal orientation or axis direction.

and wherein blocks II-IV above can be performed in any order.

In one embodiment according to the invention the design system is a system to design a guide tool 12 to be used to guide inserts tools and/or an implant or other cartilage repair objects comprises the basic blocks of:

I. Determining physical parameters for a cartilage damage in a joint and then using this information in order to;

II. Generate design parameters of a medical implant 10.

III. Generate design parameters of a guide tool 12 for use during implantation of said implant.

The physical parameters as well as the design parameters are represented as digital data that is processed or generated by specifically designed computer program code portions executed in a data processing system. The system may be fully automated or may comprise portions of computer supported manual steps of for example selections. The design parameters resulting from the process are stored in a format suitable for use as input in an automated manufacturing process.

IV. Determine placement for placement of a positioning mark 500 on the guide tool wherein the positioning mark 500 is designed to be aligned with the center 503 of said guide channel 54 in a determined joint axis 501 direction and thereby indicating a placement direction of the guide tool 12 in relation to the selected joint axis 501 during use of the guide tool 12. The direction is also indicated by placement of the positioning mark 500 of the guide tool 12 on a side of the guide channel which faces the chosen direction in relation to the joint.

The placement of the positioning mark on a guide tool, may be on top of the guide channel 54 or on top of the positioning body 11 on the side of the guide channel or at any place visible for the surgeon using the guide tool.

and wherein blocks II-IV above can be performed in any order.

In one embodiment according to the invention, the insert tools 502 and or the implant 10 is also designed to comprise a position mark 500, and the position of the position mark is designed to be on a surface which is visible for the surgeon during surgery and use of the insert tools 502 and or implant 10. Example of such surfaces are on the top of the insert tools, on a surface facing the surgeon during use of the insert tools, for example on a surface opposite to the surface facing the cartilage damage. The positioning marking 500 of an implant 10 may for example be on the articulate surface 15 of the implant, preferably not placed in the center but parted from the center of the implant or on a surface which is visible for the surgeon, or for example on a top surface of an insert tool pointing in the opposite direction compared to the cartilage contact surface 50 of the positioning body 11.

In another embodiment, the present invention relates to an individually design of surgical kit and/or a guide tool 12 comprising position marks and to a design method for design of such a kit.

In one embodiment, the placement of the position mark is determined by first determine the size, spread and placement of the cartilage contact surface in a computer model and then use this model of a cartilage contact surface and determine a direction, based on the virtual placement of the model cartilage contact surface on the simulated joint (or on an image of an individual 3D image of a joint surface). And after deciding the direction, place a virtual position mark on that place, which may be a place pointing in any direction in comparison to the placement of the guide tool in the joint, for example pointing in an anterior direction etc. The position mark is designed to be placed on a surface of the positioning body of the guide tool 12 which is a surface pointing in an opposite direction compared to the cartilage contact surface of the positioning body. The said placement of the positioning mark 500 is also determined in relation to the design of the guide channel 54 and its placement on the cartilage contact surface 50 of the guide tool 12.

This placement of said position mark on the guide tool 12 may then be used by the surgeon in order to place the individually designed guide tool in the right placement during surgery by knowing in which direction the positioning mark 500 is designed to point.

For example, if a guide tool 12 is designed to point in an anterior direction during knee surgery, and the guide tool 12 then has a positioning mark 500, placed for example on a side or on top of the guide channel or on a top surface 52 of the positioning body 12. Then the surgeon knows that the positioning mark 500 should point in an anterior direction if he placed the guide tool in a correct direction, see for an example in FIG. 2 for a placement of an implant comprising a positioning mark 500 in an anterior direction in relation to the knee joint.

A further effect of the invention is that the size of the cartilage contact surface can be designed to be smaller in area spread because the surgeon now know due to the positioning mark if the guide is placed in the correct position from start and does not need a large cartilage contact surface of the guide tool to “feel” when the guide is placed correctly.

In other embodiment, the design of the insert tools are also designed to comprise a position marking and the position marking of the insert tools is designed to coincide with the positioning mark of the guide tool 12 when the insert tools are placed within the guide tool in their first positions or their starting position. This alignment gives instruction to the surgeon about rotational start direction when using the insert tools 502.

This is exemplified in FIG. 6 wherein a height adjustment device is used as an insert tool 502 and in FIG. 6, the insert tool is placed in a starting position where both the positioning mark 500 of the insert tool is aligned with the positioning mark 500 of the guide tool 12.

See for example FIG. 2 for further examples of the invention where the implanted implant has a position mark pointing in an anterior direction compared to the joint and limb. The positioning mark 500 on the guide tool 12 used during placement of this implant also pointed in the same direction, se for example in FIG. 5.

FIG. 4-10 shows use of the guide tool of the invention together with different insert tools, FIG. 4a shows the guide tool without insert tools. FIG. 4b shows use of a drill guide 8 inside the guide channel 54 of the guide tool 12.

FIG. 5 shows the guide tool 12 together with a height adjustment device 16 inside the guide channel. A height adjustment device 16 according to the invention comprises a male part 47 and a female receiving part 48 which when used together allows for stepwise adjustment of drill depth.

In one embodiment the present invention comprises a design method for design of a surgical kit where one part is related to the design of a guide tool according to the present invention described herein and one part is directed to the design of insert tools 502 comprising positioning marks 500 which is aligned with the positioning marks of the designed guide tool when inserted in the guide tool 12 in a start position which indicating the correct rotational start position of the insert tools to the surgeon during use of the guide tool and insert tools during surgery.

FIG. 11 shows a medical implant comprising a positioning mark according to the invention and wherein the direction of the positioning mark of the implant also is indicated on the cartilage surface due to previous guidance using the guide tool according to the invention during surgery.

The present invention concerns a guide tool 12 which is designed to comprising a cartilage contact surface 52 which is individually designed to correlate to a surface and curvature in the joint. Due to this the guide tool 12 according to the invention may be correctly placed in the joint in one predetermined direction. The direction is determined during the design of the guide tool 12.

This predetermined direction may now be easier to visually see for the surgeon when he receives a guide tool according to the invention, designed to have a predetermined positioning mark, indicating a predetermined position instructing the surgeon about how he should place the guide tool 12 on the cartilage surface in the joint.

I. Determining Physical Parameters for a Cartilage Damage in a Joint.

An image or a plurality of images representing a three dimensional image of a bone member of the joint in a patient's limb may be obtained by a selected one of a per se known imaging technology for non-invasive imaging of joints, such as magnetic resonance imaging (MRI), computerized tomography (CT) imaging or a combination of both, or other suitable techniques such as delayed Gadolinium-enhanced MRI of cartilage (dGEMRIC) techniques. The image of the joint should comprise a representation of cartilage in the joint as well as the underlying subchondral bone in the area of the cartilage damage. Image data making up a three dimensional image representation of the joint is stored in a digital format in a manner that enables to keep track of the dimensions of the real joint that the image depicts.

The image data is analyzed in a data processing system to identify and determine physical parameters for the cartilage damage. The physical parameters to determine comprise the presence, the location and the size and shape of the cartilage damage, as well as curvature of the surface contour of the cartilage or the subchondral bone in an area of the cartilage damage.

In one embodiment of the inventive concept the design system operates to determine physical parameters on images of the patient's individual joint and the current cartilage damage, and thereby produces an individually designed guide tool 12. In another embodiment the design system operates on a collection of images of joints constituting a statistical basis for determining physical parameters for producing a guide tool 12 adapted for a selected location and a selected size of cartilage damage in a joint of a selected size.

The following steps, not limiting the design method according to the invention are in one exemplifying embodiment comprised in determining the physical parameters of cartilage damage:

a. Obtaining image data representing a three dimensional image of a bone member of the joint.

By way of example, a sample of a set of several images which together represents a three dimensional image of a joint.

b. Identifying in the image data cartilage damage in an articulate surface of the bone member.

In an automated process a computer program may be adapted to scan the image data for predetermined characteristics of a spot of cartilage damage in the image data. In a process with a manual part in this step an operator would visually scan a displayed image of the joint and identify a spot that has the visual characteristics of cartilage damage.

c. Determining based on the image data the location of the cartilage damage. A set of data that represents a position of the cartilage damage in the joint is selected automatically or manually. The position data is for example stored as a set of defined coordinates in the image data.

d. Determining based on the image data the size and shape of the cartilage damage. Selected measurements for size and shape of the cartilage are calculated in the image date, for example by determining a boundary line for the healthy cartilage surrounding the cartilage damage. A circular cross-section shape is preferably selected such that it covers the cartilage damage with a perimeter at a predetermined safe distance from the fringes of the damaged cartilage. The size and shape data is for example stored as a set of perimeter and thickness data with a predetermined resolution.

e. Determining based on the image data the surface contour curvature of the cartilage and/or the subchondral bone in the joint in a predetermined area comprising and surrounding the site of cartilage damage.

The curvature of the surface contour is determined for example by per se known surface matching methods in image processing. The determined curvature information can be represented as an equation or as a set of image data. The determined curvature preferably comprises two subsets of curvature information. Firstly, one subset comprises the curvature of the contour portion that comprises the cartilage damage within the cross-section shape defining the selected boundary line for the area covering the cartilage damage. Secondly, the second subset comprises the curvature of a contour portion that surrounds the site of cartilage damage, preferably comprising mutually opposing sloping parts.

II. Generating Design Parameters for a Medical Implant (10).

Based on the physical parameters for the cartilage damage, design parameters for an implant are generated by processing the physical parameters in a design stage 95 according to a predetermined scheme for the shape of an implant in the specific surgical application.

The shape and size of the implant are calculated or selected dependent on the size and shape of the cartilage damage, and dependent on the curvature of the contour of the cartilage and/or of the subchondral bone in the area substantially coinciding with the cartilage damage, optionally a positioning mark is added to the articulate surface of said implant which indicate rotational positioning to the surgeon. The positioning mark 500 of the implant 10 may for example point out a direction in relation to the joint axis 501 or other anatomic dependent direction and may point out same direction as the positioning mark on the guide tool 12 used for placing said implant.

The following steps are in one non limiting exemplified embodiment of the design method of the invention comprised in generating design parameters for a medical implant 10:

f. Generating the contour curvature for an articulate surface of an implant body 27 dependent on said determined surface curvature of the cartilage and/or the subchondral bone.

The contour curvature for the articulate surface of the implant body is generated to correspond to the curvature that covers the cartilage damage.

g. Generating a cross-section for the implant body dependent on and substantially corresponding to said determined size and shape of the damaged cartilage.

The cross-section for the implant body is generated to correspond to the cross-section shape determined for the cartilage damage.

h. Generating an edge height 14 for the implant body that substantially corresponds to the thickness of healthy cartilage plus a selected height of a bone contacting part of the implant for countersinking the implant into a recess to be made in the bone to fit and receive the implant.

A first part of the edge height 14 for the implant body 27 is generated to correspond to the determined height of the healthy cartilage, and a second part corresponds to a countersink height selected automatically according to a predetermined scheme or selected manually by an operator.

i. Optionally generating a length and a cross-section profile for an extending post 23 extending from a bone contacting surface of the implant dependent on predetermined rules related to the size and shape of the cartilage damage.

The size and shape of the extending post is selected automatically according to a predetermined scheme or is selected manually by an operator.

The image based tool may also be configured for using predetermined shapes that are adapted to the determined physical parameters to automatically or manually fit to the cartilage damage and thereby generate the design parameters.

Generating design parameters for a guide tool 12 for implanting the implant.

The design parameters for the guide are generated dependent on the physical parameters for the cartilage damage and/or dependent on the design parameters for the medical implant.

The following steps are in one exemplified embodiment of the invention comprised in generating design parameters for a medical implant:

j. Generating the contact points for a cartilage contact surface 50 of a positioning body 11 dependent on said determined surface contour curvature of the cartilage and/or the subchondral bone in the joint in a predetermined area comprising and surrounding the site of cartilage damage, such that said cartilage contact surface 50 of the positioning body corresponds to and fits to said surface contour of the cartilage or the subchondral bone in the joint.

k. Generating the cross-section profile for a guide channel 54 in a guide body 13 extending from the positioning body, said guide channel 54 passing through said positioning body 11 and said guide body 13, the cross-section profile for the guide channel being generated dependent on and substantially corresponding to said determined size and shape of the damaged cartilage, and such that the guide channel 54 is designed to have a cross-sectional profile that corresponds to the cross-section of the plate shaped implant body 27, and such that the guide channel 54 is designed to have a muzzle 29 on the cartilage contact surface 50 of the positioning body at a position corresponding to the site of the diseased cartilage.

In further exemplifying embodiments inserts tools intended to be used inside the guide channel 54 may comprise positioning marks pointing in same direction as positioning mark on the guide tool 12;

Comprising of generating the cross-section profile for an insert tool to have a cross-sectional profile that corresponds to the cross-sectional profile of the guide channel 54 with a tolerance enabling the insert tool 8 to slide within the guide channel 54 further comprising a positioning mark pointing in same direction as the positioning mark on the guide tool 12.

Further Exemplified Embodiments of Design of Insert Tools

Embodiments of the invention further comprise optional combinations of the following:

Generating design parameters for a drill bit 2 dependent on the design parameters for the extending post and such that a cross-sectional area for a drill bit is slightly smaller than the cross-sectional area for the extending post 23. Wherein the drill bit 2 is designed to comprise positioning marks pointing in same direction as the positioning mark present on the guide tool 12.

Generating design parameters for a cartilage cutting tool 6, 105 with a cross-sectional profile that is designed to correspond to the cross-sectional profile of the guide channel 54 with a tolerance enabling the cartilage cutting tool 6, to slide within the guide channel 54. Wherein the cutting tool is designed to comprise positioning marks pointing in same direction as the positioning mark present on the guide tool 12 indication in which rotational direction the cartilage cutting tool 6 should enter the guide channel 54 of the guide tool 12.

Generating design parameters for the implant comprises generating design parameters for an implant body 27 of the implant 10 being substantially flat, having a thickness 14 of approximately 0.5-5 mm.

Generating design parameters for the positioning body comprises generating design parameters for the cartilage contact surface of the positioning body having three contacting points 40, 42, 44, spread out around the guide body 13, for contacting parts of the joint in order to provide stable positioning of the guide tool 12 in the joint. Optionally designing the placement of the positioning mark on top said positioning body, so that the surgeon easily may see the mark during usage of the guide tool and wherein the positioning mark may point out a direction for placement of the guide tool in the joint in relation to the joint axis 501 or other anatomic dependent direction and may point out same direction as the positioning mark on the guide tool 12 used for placing said implant.

Generating design parameters for the guide channel 54 to have a height 31 of 3-10 cm.

Generating design parameters for the guide channel comprises generating design parameters for an orifice leading through the guide body 13 at the foot of said guide body.

Generating design parameters for a hammer tool 35 with a cross-sectional profile that is designed to correspond to the cross-sectional profile of the guide channel 54 with a tolerance enabling the hammer tool 35 to slide within the guide channel 54.

Details of the Surgical Kit

The Implant Structure

FIG. 3a-3b shows a medical implant 10 of a surgical kit according to an embodiment of the inventive concept. The plate shaped implant body 27 has an articulate surface (first surface) 15 configured to face the articulating part of the joint and a bone contact surface (second surface) 21 configured to face bone structure in the joint, the plate shaped implant body 27 has a cross-section that substantially corresponds to the area of the damaged cartilage and the articulate surface 15 has a curvature that substantially corresponds to the curvature of a healthy articulating surface at the site of diseased cartilage. The extending post 23 extends from the bone contact surface 21. Since the implant 10 of the inventive concept is custom made for a specific patient, FIG. 3a-b is an exemplifying schematic picture displaying one embodiments of the implant 10. Between the articulate surface 15 and the bone contact surface 21 there is a cartilage contacting surface 19.

The implant is specially designed, depending on the knees appearance and the shape of the damage and in order to resemble the body's own parts, having a surface which preferably corresponds to a three dimensional (3D) image of a simulated healthy cartilage surface. The implant will be tailor-made to fit each patient's damaged part of the joint.

Implant Body

The implant body 27 is substantially plate shaped, meaning that the shortest distance (represented by 24 in FIG. 3) crossing the surface 15 of the implant body 27 is substantially larger, e.g. at least 1.5 times larger than the thickness 14 of the implant body 27. By substantially plate shaped is meant that the implant body 27 may be substantially flat or may have some curvature, preferably a 3D curvature of the articulate surface 15. The articulate surface 15 may for example have a curvature that corresponds to a simulated healthy cartilage reconstructed from an image taken e.g. with MRI or CT-scanning of the damaged cartilage surface of the joint. Once the implant 10 is placed in the joint there will be a surface with no parts of the implant pointing up from or down below the surrounding cartilage—the implant is incorporated to give a smooth surface.

The area and the shape of the implant surface 15 are individual depending on the size of cartilage damage and location of the cartilage damage. The area and shape of the implant can be decided by the surgeon himself or be chosen from predetermined shapes. For instance the cross-section of the implant body 27 may have a circular or roughly circular, oval, triangular, square or irregular shape, preferably a shape without sharp edges (see FIG. 8 a-b and implant 10). The implant head or implant body 27 can vary in size and shape and are adjusted to the size and shape of the damaged cartilage tissue and to the needs of particular treatment situations. The size of the implant 10 may also vary. The area of the articulate surface 15 of the implant varies in different realizations of the inventive concept between 0.5 cm² and 20 cm², between 0.5 cm² and 15 cm², between 0.5 cm² and 10 cm², between 1 cm² and 5 cm² or preferably between about 0.5 cm² and 5 cm².

In general, small implants are preferred since they have a smaller impact on the joint at the site of incision and are also more easily implanted using arthroscopy or smaller open surgical procedures. The primary factor for determining the size of the implant is however the nature of the lesion to be repaired.

The Extending Post

The implant replaces an area of damaged cartilage in an articulating surface of a joint. Before the implant is placed in the desired position, the damaged cartilage is removed and also a part of the bone beneath, i.e. a recess fitting the implant is made in the bone. Furthermore, a hole can be drilled in the bone to fit the implant structure. The extending post of the implant or the rod-part 23 of the implant 10, is used for securing the implant 10 in the drilled hole of the bone. The length 22 of the extending post 23, extending from the implant head 27, is adjusted to a length needed to secure the implant 10 in the bone. The extending post 23 is intended to give a primary fixation of the implant 10, it provides mechanical attachment of the implant 10 to the bone in immediate connection with the surgical operation.

The position of the extending post 23 on the bone contact surface 21 can be anywhere on the bone contact surface 21 or the extending post 23 may have a central position.

The extending post 23 has a physical structure in the form of for example a cylinder or other shapes such as one or more of a small screw, peg, keel, barb or the like.

In one embodiment, the extending post 23 has a positioning part 25, where the positioning part 25 is located distal to the plate shaped implant body 27. The longitudinal symmetry axes of the first part of the extending post 23 and the positioning part 25 coincide. The diameter of the positioning part 25 is smaller than the diameter of the first part of the extending post 23.

The Guide-Tool

FIG. 13a-b shows exemplifying embodiments of a guide-tool 12. Other examples of guide tools according to the invention is The guide tool 12 comprises a positioning body 11 and a guide body 13, with a guide channel 54 through said guide body 13 and positioning body 11. The positioning body has a cartilage contact surface 50 that has a shape and contour that is designed to correspond to and to fit the contour of the cartilage or the subchondral bone in the joint in a predetermined area surrounding the site of diseased cartilage. The guide tool 12 also has a top surface 52 facing the opposite direction compared to the cartilage contacting surface 50. The guide body 13 extends from said top surface 52 of the guide tool 12.

The guide channel 54 has an inner cross-sectional profile that is designed to correspond to the cross-section of the plate shaped implant body 10. In other words, the plate shaped implant body 10 fits the guide channel 54, with a slight tolerance to allow a sliding movement of the implant in the guide channel 54. The positioning body 11 has a mouth or muzzle 29 which is the guide channel's 54 opening on the cartilage contact surface 50. The mouth 29 is in a position on the cartilage contact surface 50, corresponding to the site of the diseased cartilage in a joint. The height 31 of the guide channel 54 must be sufficiently long to give support to the tools used inside the guide body 13. The height 31 is preferably higher than the thickness of the surrounding tissue. In this way, the opening of the guide channel 54 is easy to access for the surgeon. The height 31 of the guide channel 54 is between 1 and 10 cm, preferably 3-10 cm, and always sufficiently high to ensure stabilization of the tools that are to be inserted into the guide channel 54.

The guide tool 12 is easy to place due to the precise fit of the positioning body 11 on the cartilage surface. The guide tool 12 is designed to be inserted in as lesion which is as small as possible to be able to repair the specific cartilage damage. The height 31 of the guide channel 54 is sufficiently high to be easily accessible for the surgeon during surgery. In one embodiment, the top of the guide channel 54 is designed to project above the tissue surrounding the surgery cut when the guide tool is placed on the cartilage in a joint during surgery.

The size and shape of cartilage contact surface 50 of the guide tool 12 is determined depending on the size and shape of the damaged cartilage and thus on the cross section of the implant body 10 and the guide channel 54, and also depending on the position of the cartilage area in a joint. The size, shape or spread of the surface 50 is a consideration between the following aspects; minimize surgery lesion, maximize stability for guide tool 12, anatomic limitations on the site of the injury. Not all cartilage surfaces in a joint can be used for placement of the guide tool. A large spread of the cartilage contact surface 50 is to prefer to get good stability of the guide tool, however, a large surface area of the surface 50 may also lead to a large surgical intervention which is undesired. Thus the size of the cartilage contact surface 50 and of the positioning body 13 is determined by a balance between the desire to achieve good positioning stability and small surgical operations. Also, the cartilage contact surface 50 need not have a continuous, regular shape, but may have an irregular shape, as long as it gives adequate support and stable positioning of the guide tool 12. The cartilage contact surface may also consist of three separated points.

When designing the guide tool, the cartilage contact surface 50 can be designed to cover three points (40, 42, 44 for an example, see FIG. 13b ) distributed over the cartilage surface of the joint where the implant is to be inserted. The points are chosen to give maximum support and positional stability for the positioning body 11 and thus these points, either decided and identified by the surgeon or automatically identified by design software, serve the ground when designing the surface 50 of the guide tool 12. The cartilage contact surface 50 can also be formed such that it uses the curvature in the cartilage surface in a joint for stability. For example, in a knee joint, the condyles are separated from each other by a shallow depression, the posterior intercondyloid fossa, this curvature together with the medial epicondyle surface can be used to give the cartilage contact surface 50 a stabile attachment to the cartilage surface in a knee joint. The cartilage contact surface does not need to be a continuous, regular surface but preferably has the three points exemplified by 40, 42 and 44 for stability. Optionally the cartilage contacting surface 50 can be further stabilized by attachment with nails, rivets or similar attachment means to the bone surrounding the cartilage in a joint (see FIG. 4b ). This additional attachment with rivets 48 or the like gives additional support and stability and also gives the possibility to keep the cartilage contact surface as small as possible. The position of the rivets may be predetermined and marked out on the surface 50 by premade drill holes 33.

The guide-tool 12 aids with exact precision removal of a volume of cartilage and subchondral bone and the guide tool 12 also guides the placement of the implant 10 in for example a knee. Placement of an exemplified embodiment of the guide-tool 12 on the cartilage surface on a knee can be seen in FIG. 13 a.

The guide body 13 comprises an orifice, see FIG. 11, at the foot of the guide body that leads from the guide channel into the open outside the guide body. The orifice 145 is designed to enable output of waste such as cartilage tissue and bone chips from boring or reaming in the preparation of the recess for the implant in the joint. The orifice is preferably also designed to enable visual inspection into the implant site during surgical operation.

The guide tool according to the present invention is further designed to comprise a positioning mark 500, comprised in the structure of the positioning body or guide body or guide channel construction of the guide tool and wherein the positioning mark is aligned with the center 503 of the guide channel 54 in a chosen joint axis 501 direction.

The guide tool 12 may be placed in the joint using pins 506 and clams 507 for stabilization and fastening see for example in FIG. 7.

The Insert Tool 502

The insert tool 502 is in different embodiments of the invention for example selected from; the cartilage cutting tool, the punch, the cartilage cut drill, the reamer guide, the drill guide or the hammer tool, implant dummy, cartilage cutter. The insert tool is used inside the guide channel 54 of the guide tool 12 and fits in the guide channel 54, with a slight tolerance to allow a sliding movement of the insert tool in the guide channel 54. The cross-sectional profile, and thus the circumferential shape of the insert tool, corresponds to the chosen cross-section of the implant surface 15 in size and shape

The Cartilage Cutting Tool

The cartilage cutting tool is a tool which is used to cut the cartilage in the joint around the area of damaged cartilage to prepare for the insertion of the implant. The cartilage cutting tool may for example be a punch 6 or a cartilage cut drill 105. It is used inside the guide channel 54 of the guide tool 12 and fits in the guide channel 54, with a slight tolerance to allow a sliding movement of the cartilage cutting tool in the guide channel 54. The cartilage cutting tool preferably cuts the cartilage so that the cut edges of the cartilage are sharp and smooth. These sharp and smooth edges are of great importance when the implant is placed into the prepared recess in the cartilage and bone. In one embodiment the cartilage cutting tool, in addition to cutting the cartilage, may also cut/carve/drill the underlying bone. A hole in the cartilage which is cut (punched or drilled) with the cartilage cutting tool according to the inventive concept ends up with a precise fit of the implant into the prepared cartilage since the cartilage cutting tool allows for an exact, precise cut. The recess in the cartilage and/or bone, made by the cartilage cutting tool always correspond to the chosen cross-section of the implant surface 15 in size and shape

In one exemplifying embodiment of the inventive concept the cartilage cutting tool is a punch 6. The punch 6 is a solid body with a hollow shape or recess 5 in one end. The recess 5 has sharp edges 60. The punch 6 is used to punch out and remove the damaged cartilage from the joint. The punch is to be placed inside the guide channel 54 of the guide tool 12, with the recess pointing down onto the cartilage. A hammer is then used to hammer the punch recess 5 through the cartilage. In this way the damaged cartilage is removed by punching. The depth 59 of the recess 5 on the punch 6 may be adjusted to the individual person's cartilage thickness. It is of great importance that the punch has sharp cutting edges 60.

The punch 6 fits the inside of the guide channel 54, with a slight tolerance to allow a sliding movement of the punch in the guide channel 54. The fit ensures the correct, desired placement of the punch on the cartilage surface and thus the precise removal of the damaged cartilage area. The punch preferably gives sharp precise edges of the remaining cartilage in the joint surrounding the removed cartilage piece, which is of importance when placing the implant 10 in the joint. The contour of the cutting edge 60, i.e. the contour of the surface of the cutting edge 60 that is to face and cut the cartilage, is in one embodiment designed to match the contour of the patient's cartilage and/or bone at the site of the joint where the punch is to cut. This further ensures that the cartilage will be properly and efficiently cut, giving sharp precise edges of the remaining cartilage as well as minimized damage to the underlying bone.

The length 56 of the punch 6 is in one embodiment longer than the height 31 of the guide channel 54. The length 56 of the punch 6 is preferably between 4 and 12 cm.

The cross-sectional profile, and thus the circumferential shape of the cutting edge 60, of the punch 6 corresponds to the chosen cross-section of the implant surface 15 in size and shape The cross-sectional profile of the punch varies in different realizations of the inventive concept between 0.5 cm² and 20 cm², between 0.5 cm² and 15 cm², between 0.5 cm² and 10 cm² or preferably between about 1 cm² and 5 cm².

In one exemplifying embodiment of the inventive concept the cartilage cutting tool is a cartilage cut drill. The cartilage cut drill is used to cut the cartilage in the joint around the area of damaged cartilage to prepare for the insertion of the implant with a cut-drill technique.

The cartilage cut drill 105 is a drill, with a drill body 111 and with sharp cutting edges 108 and a center marker 106. The cartilage cut drill 105 has a cross-sectional profile that is designed to correspond to the inner cross-sectional profile of the guide channel 54 with a tolerance enabling cartilage cut drill body 111 to slide within the guide channel 54. Also, the cross-sectional profile is designed to correspond to the cross-section of the implant.

The Reamer Guide

In one embodiment of the inventive concept the surgical kit comprises a reamer guide that is placed in the guide channel 54 before reaming the recess in the bone. The reamer guide placed in the guide channel 54 protects the cartilage surrounding the implant site while the reamer bit 4 is used inside the guide channel 54 of the guide tool 12.

The reamer guide 28, is a channel shaped structure with thin walls designed to fit the inside of the guide channel 54, with a slight tolerance to allow a sliding movement of the reamer guide 28 in the guide channel 54. In other words, the cross sectional profile of the reamer guide 28 fits the cross sectional profile of the guide channel 54 such that the reamer guide 28 may be used as a lining, lining the insides of the guide channel 54 (see FIG. 8). The walls of the reamer guide 28 have a thickness of less than 1 mm. The reamer guide 28 preferably has a height 66 that is at least the height achieved by adding the inner height 31 of the guide channel 54 with the height 59 of the recess 5 of the punch 6.

The Height Adjustment Device or Insert Tool

A height adjustment device 16 according to the invention comprises a male part 47 and a female receiving part 48 which when used together allows for stepwise adjustment of drill depth.

The male part is in the outermost position in a zero-mode and may from there be adjusted inwards allowing the surgeon stepwise the for example make stepwise deeper drill holes. When the height adjustment device 16 is in starting mode or outermost zero-mode the positioning marking of the guide tool 12 and the positioning marking of the height adjustment device are aligned, se for example FIG. 6.

Thus, by being able to adjust the length 31 of the guide channel the surgeon is also able to adjust the depth of drilling and cutting into the bone. The length 31 of the guide channel may be varied since the guide body 13 and the height adjustment device 16 parts are able to move in relation to one another. Further, the male part 47 and the female receiving part 48 of the height adjustment device may be arranged such that the length 31 of the guide channel may be varied at certain stepwise intervals 115, e.g. at 200 μm or at 100-300 μm intervals or steps, or any other desired interval, see for example FIG. 16. For example the height might be adjusted between for example 0.2-3 mm, in one or several steps. This may for instance be achieved by arranging the male part 47 inside the female receiving part 48 of the height adjustment device 16 such that the male part 47 insert tool to have a cross-sectional profile that corresponds to the cross-sectional profile of the female part guide channel 120 with a tolerance enabling the insert tool to slide within the guide female part guide channel 120. For example, the construction may be arranged such that the guide body 13 and height adjustment device 16 may be turned in relation to one another at preset steps, by lifting the male part sot that the protruding ridges may slip out of one groove and enter another groove. When the male part 47 is fitted in the female part their position are locked in relation to each other or prone to hook each other at those intervals. The female part comprises grooves or ledges 17 at different heights relative to the positioning body of the guide tool. The male part 47 comprises a guide channel 54 inside the male part 47, the guide channel 54 may be cylinder shaped and protruding ridges 105 on the outer surface of the male part 47. When the male part 47 is placed inside the female receiving part 48 the protruding ridges 105 of the male part 47 are placed or located inside one of the grooves 17 on the female receiving part 48. The position of the grooves 17 and the position of the ridges 105 in relation to the positioning body or the cartilage contact surface 50 adjust or regulate the length 31 of the guide body 13. The height adjustment device 16 may be used by the surgeon to adjust the depth of drilling, e.g. by increasing the drill depth in steps at the preset intervals. The height adjustment device 16 may advantageously be used together with an implant dummy 36, as described below, to make sure that the drill depth in the bone matches the height 14 of the implant body 27. This ensures that the articulate surface 15 of the implant 10 will be in line with the surrounding cartilage at the site of implantation once implanted.

The Drill-Guide

In one embodiment of the inventive concept the surgical kit comprises a drill guide 8 that is used to direct a drill for drilling a hole in the bone at the site of cartilage damage, for fastening of the extending post 23 of the implant 10 in the bone tissue. The drill guide 8 comprises a drill guide body and a guide channel 7 passing through the drill guide body. The guide channel 7 is designed to receive and guide the drill during the surgical procedure. The drill guide 8 is designed to fit the inside of the guide channel 54, with a slight tolerance to allow a sliding movement of the drill guide 8 in the guide channel 54, see FIG. 8a-b . In other words, the cross-sectional profile of the drill guide body matches the cross-sectional profile of the guide channel 54 The fit ensures the correct, desired placement of the drill guide 8 on the cartilage surface and thus ensures the precise direction and placement of the drill hole in the bone.

The guide channel 7 is designed to be positioned in the drill guide body such that the position corresponds to the desired position of the drill hole in the bone. The positioning of the guide channel 7 in the drill guide 8 is coordinated with the positioning of the extending post 23 on the bone contacting surface 21 of the implant to ensure correct positioning of the implant in the bone.

The length 62 of the drill guide 8 and thus the drill channel 7 is longer than the height 31 of the guide channel 54. The length is preferably 4-12 cm.

The cartilage contacting surface 64 of the drill guide 8 corresponds to the chosen implant surface 15 in size and shape. The surface 64 varies in different realizations of the inventive concept between 0.5 cm² and 20 cm², between 0.5 cm² and 15 cm², between 0.5 cm² and 10 cm² or preferably between about 1 cm² and 5 cm². In one embodiment the cartilage contacting surface 64 of the drill guide 8 is designed to match the contour of the patient's cartilage and/or bone at the site of the joint where the implant is to be inserted.

See FIG. 9c for a demonstration of how the drill-guide 8 fits inside the guide-channel 54 of the guide-tool 12.

Drill-Bit

The surgical kit of the present inventive concept may also comprise a drill-bit 2, see FIG. 12. The drill-bit 2 may have an adjustable depth gauge 1. The depth gauge 1 on the drill-bit 2 is supported by the top 30 of the guide channel 54 and by using this support the depth of the drill hole can be controlled. The drill-bit 2 fits inside the drill channel 7 in the drill-guide 8 to give a drill-hole in the bone with an exact position and depth and where the depth is depending on the placement of the depth gauge 1 on the drill-bit 2, and also depending on the height of the guide-channel 31.

Reamer-Bit

The surgical kit of the present inventive concept may also comprise a reamer-bit. The reamer-bit 4 may have a depth gauge 3. The reamer bit 4 is used together with the guide-tool 12 and possibly the reamer guide 28. The reamer-bit 4 is used inside the guide channel 54, removing bone tissue, aided by the guide channel 54 and possibly the reamer guide 28. The depth gauge 3 on the reamer-bit 4 is supported by the top 30 of the guide channel 54 and by using this support the depth of the reamed bone recess can be controlled. The depth of the reamed recess in the bone is depending on the placement of the depth gauge 3 on the reamer-bit 4, and also depending on the height 31 of the guide-channel 54. The depth of the reamed surface is determined depending on the injury and on the desired implants size.

Hammer Tool

The optional hammer tool 35 (see FIG. 12) consists of a solid body and is designed to fit the inside of the guide channel 54, with a slight tolerance to allow a sliding movement of the hammer tool 35 in the guide channel 54, see FIG. 8. The hammer tool 35 is used inside the guide channel 54 to hammer the implant in place. The height of the hammer tool 68 is the same height 62 as of the drill guide 8. Once the hammer tool is hammered in the same level as the top of the guide channel, the hammering and thus the placement of the implant is finished.

Implant Dummy and Dummy Reference

The implant dummy 36 and dummy reference 37, see FIG. 12, are used to make sure that the cut, carved or drilled recess in the bone that is to receive the implant body 27, is deep enough to fit the implant. This is very important, since the articulate surface 15 of the implant 10 must not project over the surface of the surrounding cartilage tissue. If it would it could cause a lot of damage to the surrounding cartilage and to the cartilage on the opposite side of the joint. Preferably the articulate surface 15 should form a continuous surface with the surrounding cartilage, neither projecting above nor being sunken below the surface of the surrounding cartilage. The checking of the recess depth is difficult or impossible to do with the implant 10 itself, since the implant 10, e.g. with its extending post 23, is designed to be fixed in the bone once inserted, and thus is difficult or impossible to remove. The implant dummy, on the other hand, is designed for easy removal from the recess once the recess depth has been checked.

The implant dummy 36, see FIG. 12, has an implant element 41 that is designed to match the implant body 27. The lower surface 41 a of the implant element 41 is a replica of the bone contact surface 21 of the implant that is to be implanted. That is, if the implant 10 and bone contact surface 21 is custom made for the specific patient, the implant element 41 and its lower surface 41 a will also be custom made and the lower surface 41 a be a replica of the bone contact surface. The cross-sectional profile of the implant element 41 corresponds to the cross-sectional surface of the implant body, or is slightly smaller in order to ensure easy removal of the implant dummy from the recess.

The implant dummy 36 also has a top surface. The distance between the lower surface of the implant element 41 and the top surface corresponds to the distance that you get when adding the thickness 14 of the implant body 27 (corresponding to the depth of the recess in the bone plus the thickness of the corresponding cartilage). The dummy reference 37, see FIG. 12, is arranged to fit to, and possibly releasable attach to, the guide hole 53 of the guide base 12, see.

To ensure that the implant dummy 36 is placed in a correct orientation in the recess of the bone, i.e. in an orientation that corresponds to the orientation that the implant 10 is to be inserted in, the top surface 43 and/or the implant element 41 may be provided with positioning mark 500. A corresponding positioning mark 500 is provided also on the implant dummy 36 and on the guide base 12. 

The invention claimed is:
 1. A method for designing a surface implant, comprising: designing a contour curvature of the surface implant so that an articulate surface of the surface implant is designed to correspond to a simulated healthy cartilage surface reconstructed from a 3D model based on one or more images taken with MRI or CT-scanning of a damaged cartilage surface of a joint, wherein the designing of the contour curvature of the surface implant includes designing the contour curvature to be patient customized in that the articulate surface of the implant corresponds to the simulated healthy cartilage; designing a positioning mark on a surface of the surface implant so that the direction of the positioning of the mark on the contour curvature of the surface implant, corresponding to the simulated healthy cartilage, is determining the rotational positioning of the surface implant in which the contour curvature of the surface implant corresponds to the simulated healthy cartilage surface; and providing the positioning mark on a surface of the surface implant such that the positioning mark is parted from the center of the implant to be visible for a surgeon and is adapted to be used for indicating said rotational position of the surface implant to the surgeon.
 2. The method according to claim 1, further comprising: designing the positioning mark of the implant to be pointing in an anterior direction compared to the joint.
 3. The method according to claim 1, further comprising: designing the positioning mark of the implant so that the direction of the positioning mark on the contour curvature of the implant is determining the rotational positioning of the implant in that said rotational positioning is also indicated on a cartilage surface due to a previous guidance using a guide tool.
 4. The method according to claim 1, further comprising: designing the shape and size of the implant dependent on the size and shape of the damaged cartilage surface of the joint and dependent on curvature of the simulated healthy cartilage surface; and designing the positioning mark to point out a direction in relation to an anatomic dependent direction.
 5. The method according to claim 1, further comprising: designing the shape and size of the implant dependent on the size and shape of the damaged cartilage surface of the joint and dependent on curvature of the simulated healthy cartilage surface; and designing the positioning mark to point out the same direction, or joint axis, as a positioning mark on a guide tool to be used for placing said implant. 